Several air heaters have exploited the fact that air is warmed as it flows turbulently through the blades of a blower or pump. The temperature increase in a single pass of the air through blower blades is usually tiny, however, so that practically useful increases in air temperature have required that the air pass many times through the blower blades. Although this gradually heats the air, it greatly diminishes the ability of the blower to move the air elsewhere.
We have found a way of heating air effectively in a multi-stage blower that can also pump air at a flow rate adequate to serve as a space heater. Each stage of our heater is especially effective in heating air and can achieve at least a 10.degree. temperature rise--to require only a few stages for a practically usable temperature increase. Since the air passes only once through each stage, our heater is also effective as a through-flow pump that can distribute heated air through ducts in a building. Our heater heats return air without changing moisture content or causing any odor; and since it has no high temperature region, it is safe and practical in explosive or flammable environments.